The U.S. Renewable Fuel Standards (RFS) mandate requires increasing volumes of advanced biofuels to be produced. One method being developed to meet this mandate is the fast pyrolysis of biomass. Conventional biomass fast pyrolysis requires rapid heating of biomass in the absence of oxygen. Products include a solid carbonaceous char that retains the vast majority of metals (e.g. Na, K, Mg) present in the biomass feedstock. Conventional fast pyrolysis also produces oxygenated pyrolysis vapors that are highly reactive, and product compounds comprising radicals can lead to rapid, uncontrolled oligomerization or polymerization to form large molecular weight compounds that are extremely difficult to upgrade to transportation fuels. There is a need to improve fast pyrolysis technology to allow for rapid stabilization or upgrading of the raw pyrolysis vapors to prevent uncontrolled polymerization, while still allowing some intermolecular addition reactions to proceed, thereby efficiently producing hydrocarbons having molecular weights and characteristics fungible with current hydrocarbon transportation fuels, while simultaneously preventing char and associated catalyst poisons from contacting upgrading catalysts that convert these primary products.